A ferrous oxalate mediated photo-Fenton system: Toward an increased biodegradability of indigo dyed wastewaters

This study assessed the applicability of a ferrous oxalate mediated photo-Fenton pretreatment for indigo-dyed wastewaters as to produce a biodegradable enough effluent, likely of being derived to conventional biological processes. The photochemical treatment was performed with ferrous oxalate and hydrogen peroxide in a Compound Parabolic Concentrator (CPC) under batch operation conditions. The reaction was studied at natural pH conditions (5–6) with indigo concentrations in the range of 6.67–33.33 mg L−1, using a fixed oxalate-to-iron mass ratio (C2O42−/Fe2+ = 35) and assessing the system's biodegradability at low (257 mg L−1) and high (1280 mg L−1) H2O2 concentrations. In order to seek the optimal conditions for the treatment of indigo dyed wastewaters, an experimental design consisting in a statistical surface response approach was carried out. This analysis revealed that the best removal efficiencies for Total Organic Carbon (TOC) were obtained for low peroxide doses. In general it was observed that after 20 kJ L−1, almost every treated effluent increased its biodegradability from a BOD5/COD value of 0.4. This increase in the biodegradability was confirmed by the presence of short chain carboxylic acids as intermediate products and by the mineralization of organic nitrogen into nitrate. Finally, an overall decrease in the LC50 for Artemia salina indicated a successful detoxification of the effluent.

Tratamientos avanzados de agua potable para eliminación de materia orgánica disuelta : aplicación del BAC

Los procesos de biofiltración por carbón activo biológico se han utilizado desde hace décadas, primeramente en Europa y después en Norte América, sin embargo no hay parámetros de diseño y operación específicos que se puedan utilizar de guía para la biofiltración. Además, el factor coste a la hora de elegir el carbón activo como medio de filtración impacta en el presupuesto, debido al elevado coste de inversión y de regeneración. A la hora de diseñar y operar filtros de carbón activo los requisitos que comúnmente se buscan son eliminar materia orgánica, olor, y sabor de agua. Dentro de la eliminación de materia orgánica se precisa la eliminación necesaria para evitar subproductos en la desinfección no deseados, y reducir los niveles de carbono orgánico disuelto biodegradable y asimilable a valores que consigan la bioestabilidad del agua producto, a fin de evitar recrecimiento de biofilm en las redes de distribución. El ozono se ha utilizado durante años como un oxidante previo a la biofiltración para reducir el olor, sabor, y color del agua, oxidando la materia orgánica convirtiendo los compuestos no biodegradables y lentamente biodegradables en biodegradables, consiguiendo que puedan ser posteriormente eliminados biológicamente en los filtros de carbón activo. Sin embargo la inestabilidad del ozono en el agua hace que se produzcan ácidos carboxilos, alcoholes y aldehídos, conocidos como subproductos de la desinfección. Con esta tesis se pretende dar respuesta principalmente a los siguientes objetivos: análisis de parámetros requeridos para el diseño de los filtros de carbón activo biológicos, necesidades de ozonización previa a la filtración, y comportamiento de la biofiltración en un sistema compuesto de coagulación sobre un filtro de carbón activo biológico. Los resultados obtenidos muestran que la biofiltración es un proceso que encaja perfectamente con los parámetros de diseño de plantas con filtración convencional. Aunque la capacidad de eliminación de materia orgánica se reduce a medida que el filtro se satura y entra en la fase biológica, la biodegradación en esta fase se mantienen estable y perdura a lo lago de los meses sin preocupaciones por la regeneración del carbón. Los valores de carbono orgánico disuelto biodegradable se mantienen por debajo de los marcados en la literatura existente para agua bioestable, lo que hace innecesaria la dosificación de ozono previa a la biofiltración. La adición de la coagulación con la corrección de pH sobre el carbón activo consigue una mejora en la reducción de la materia orgánica, sin afectar a la biodegradación del carbón activo, cumpliendo también con los requerimientos de turbidez a la salida de filtración. Lo que plantea importantes ventajas para el proceso. Granular activated carbon filters have been used for many years to treat and produce drinking water using the adsorption capacity of carbon, replacing it once the carbon lost its adsorption capacity and became saturated. On the other hand, biological activated carbon filters have been studied for decades, firstly in Europe and subsequently in North America, nevertheless are no generally accepted design and operational parameters documented to be used as design guidance for biofiltration. Perhaps this is because of the cost factor; to choose activated carbon as a filtration media requires a significant investment due to the high capital and regeneration costs. When activated carbon filters are typically required it is for the reduction of an organic load, removal of colour, taste and / or odour. In terms of organic matter reduction, the primary aim is to achieve as much removal as possible to reduce or avoid the introduction of disinfection by products, the required removal in biodegradable dissolved organic carbon and assimilable organic carbon to produce a biologically stable potable water which prohibits the regrowth of biofilm in the distribution systems. The ozone has historically been used as an oxidant to reduce colour, taste and odour by oxidizing the organic matter and increasing the biodegradability of the organic matter, enhancing the effectiveness of organic removal in downstream biological activated carbon filters. Unfortunately, ozone is unstable in water and reacts with organic matter producing carboxylic acids, alcohols, and aldehydes, known as disinfection by products. This thesis has the following objectives: determination of the required parameters for the design of the biological activated filters, the requirement of ozonization as a pre-treatment for the biological activated filters, and a performance assessment of biofiltration when coagulation is applied as a pretreatment for biological activated carbon filters. The results show that the process design parameters of biofiltration are compatible with those of conventional filtration. The organic matter removal reduces its effectiveness as soon as the filter is saturated and the biological stage starts, but the biodegradation continues steadily and lasts for a long period of time without the need of carbon regeneration. The removal of the biodegradable dissolved organic carbon is enough to produce a biostable water according to the values shown on the existing literature; therefore ozone is not required prior to the filtration. Furthermore, the addition of coagulant and pH control before the biological activated carbon filter achieves a additional removal of organic matter, without affecting the biodegradation that occurs in the activated carbon whilst also complying with the required turbidity removal.